The photos were presented as evidence during a bail hearing Thursday in Honolulu. A federal judge ruled that Kang would remain in custody without bail following a request by federal officials.

Prosecutors argued Kang could pose a danger to the community and that he is a substantial flight risk, CNN affiliate KHON-TV in Honolulu reported.

His next court appearance is scheduled for July 24.

Kang, who was stationed at Schofield Barracks in Hawaii, was investigated by the FBI and Army for more than a year, the FBI said in a statement.

The FBI said it believed he was a "lone actor."

Kang's father arrived at the hearing Thursday in hopes of having a chance to talk to his son.

"Just hold in there. You have a support group," Clifford Kang told KHON he would tell his son after learning he wouldn't be able to contact him. "Just relax and I'll be there for him. Just like the old Navy saying, we don't leave our men behind."

A decorated veteran

The younger Kang is an active-duty Army air traffic control operator assigned to the 25th Infantry Division at Wheeler Army Airfield in Hawaii. Kang's service records show he was deployed to Afghanistan from July 2013 to April 2014 and served in Iraq from March 2010 to February 2011. He has received a range of honors for his service, including the Army Commendation Medal.

An attorney representing Kang indicated his client had possible mental health issues that had gone untreated.

"It would appear that Sgt. Kang, a decorated veteran of two deployments to the Middle East, may have some service-related mental health issues which the government was aware of, but neglected to treat," the lawyer, Birney Bervar, said in an email.

On Thursday, Bervar told KHON he plans to have Kang undergo a mental health evaluation.

"The government should have offered a hand to pull him back, but instead it looks like they just pushed him and pushed him and pushed him." he said. "It looks to me that they've exploited his mental illness and has thrown gasoline on the fire of his mental illness to get him to commit a crime that they could arrest him for."

His apparent radicalization

The criminal complaint filed against Kang alleges he swore allegiance to ISIS and tried to provide ISIS with both military documents and training. The complaint said Kang made threats and pro-ISIS arguments while in the Army and that his security clearance was revoked temporarily in response to those actions in 2012.

The Army noted his apparent radicalization to the FBI last year. After his arrest, Kang waived his Miranda rights, admitted he had pledged to join ISIS and attempted to aid the group, according to the complaint.

The complaint alleges Kang spoke with undercover FBI agents purporting to be connected to ISIS. It says that Kang told one agent about a desire to join ISIS and offered to provide military documents and demonstrate martial arts techniques to another agent.

In May, a US Air Force veteran was sentenced to 35 years in prison for attempting to join ISIS. Authorities arrested Tairod Pugh in New Jersey in 2015.